Pulmonary Function Tests

Also known as Lung Function Tests
Pulmonary function tests, or PFTs, measure how well your lungs work.

They include tests that measure lung size and air flow, such as spirometry and lung volume tests. Other tests measure how well gases such as oxygen get in and out of your blood. These tests include pulse oximetry and arterial blood gas tests. Another pulmonary function test, called fractional exhaled nitric oxide (FeNO), measures nitric oxide, which is a marker for inflammation in the lungs. You may have one or more of these tests to diagnose lung and airway diseases, compare your lung function to expected levels of function, monitor if your disease is stable or worsening, and see if your treatment is working.

The purpose, procedure, discomfort, and risks of each test will vary.

  • Spirometry measures the rate of air flow and estimates lung size. For this test, you will breathe multiple times, with regular and maximal effort, through a tube that is connected to a computer. Some people feel lightheaded or tired from the required breathing effort.
  • Lung volume tests are the most accurate way to measure how much air your lungs can hold. The procedure is similar to spirometry, except that you will be in a small room with clear walls. Some people feel lightheaded or tired from the required breathing effort.
  • Lung diffusion capacity assesses how well oxygen gets into the blood from the air you breathe. For this test, you will breathe in and out through a tube for several minutes without having to breathe intensely. You also may need to have blood drawn to measure the level of hemoglobin in your blood.
  • Pulse oximetry estimates oxygen levels in your blood. For this test, a probe will be placed on your finger or another skin surface such as your ear. It causes no pain and has few or no risks.
  • Arterial blood gas tests directly measure the levels of gases, such as oxygen and carbon dioxide, in your blood. Arterial blood gas tests are usually performed in a hospital, but may be done in a doctor’s office. For this test, blood will be taken from an artery, usually in the wrist where your pulse is measured. You may feel brief pain when the needle is inserted or when a tube attached to the needle fills with blood. It is possible to have bleeding or infection where the needle was inserted.
  • Fractional exhaled nitric oxide tests measure how much nitric oxide is in the air that you exhale. For this test, you will breathe out into a tube that is connected to the portable device. It requires steady but not intense breathing. It has few or no risks.

Other tests may be needed to assess lung function in infants, children, or patients who are not able to perform spirometry and lung volume tests. Before your tests, you may be asked to not eat some foods or take certain medicines that can affect some pulmonary function test results.

Visit Pulmonary function tests and Blood gases for more information about this topic.

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